linux-kernel - Re: [FYI] tux3: Core changes

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Message-ID: <5564E76D.7080901@redhat.com>
Date:	Tue, 26 May 2015 17:36:45 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Daniel Phillips <daniel@...nq.net>, Jan Kara <jack@...e.cz>
CC:	David Lang <david@...g.hm>, tux3@...3.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [FYI] tux3: Core changes

On 05/26/2015 04:22 PM, Daniel Phillips wrote:
> On 05/26/2015 02:00 AM, Jan Kara wrote:

>> So my opinion is: Don't fork the page if page_count is elevated. You can
>> just wait for the IO if you need stable pages in that case. It's slow but
>> it's safe and it should be pretty rare. Is there any problem with that?
> 
> That would be our fallback if anybody discovers a specific case where page
> fork breaks something, which so far has not been demonstrated.
> 
> With a known fallback, it is hard to see why we should delay merging over
> that. Perfection has never been a requirement for merging filesystems. On

However, avoiding data corruption by erring on the side of safety is
a pretty basic requirement.

> the contrary, imperfection is a reason for merging, so that the many
> eyeballs effect may prove its value.

If you skip the page fork when there is an elevated page count, tux3
should be safe (at least from that aspect). Only do the COW when there
is no "strange" use of the page going on.

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